class Car:
    
    def __init__(self):
        self.name = raw_input("enter car name: ")

    def driveForward(self):
        print "%s driving forward..." % self.name
        print "completed"

    def driveBackward(self):
        print "%s driving backward..." % self.name
        print "completed"

class Truck(Car):
    
    def __init__(self):
        self.name = raw_input("enter truck name: ")
        self.cargo = None

    def loadCargo(self):
        self.cargo = raw_input("what cargo do you wish to load?:")
        print "loading %s" % self.cargo
        print "completed"

    def unloadCargo(self):
        if self.cargo == None:
            print "no cargo to unload"

        else:
            print "unloading %s" % self.cargo
            self.cargo = None
            print "completed"